In recent years, users reading or browsing documents by using an image display apparatus such as a tablet terminal and a smartphone have increased. On such an image display apparatus, a document having a plurality of pages can be displayed by switching pages one by one. In addition, on an image display apparatus equipped with a touch panel which accepts a handwriting input performed by a user, information (hereinafter, referred to as handwriting information) including characters and figures handwritten by a user can be displayed together with a document.
Regarding such an image display apparatus, for example, Japanese Laid-Open Patent Application Publication (JP-A) No. 2012-173988 discloses the following data processing apparatus. The image processing apparatus includes an input section configured to accept an input operation related to preparation of a document, a display section, and a processing section. The processing section has: a function for displaying a document under preparation on the display section; a function for displaying, when an operation for specifying reference data is accepted during preparation of the document, the specified reference data on the display section together with the document; a function for generating, when a predetermined operation is received in a situation that a document under preparation and reference data are displayed on the display section, linking information which associates a position in the document at which the most recent information is written in the document after the reference data is displayed with the reference data; and a function for storing a prepared document and the linking information in a predetermined storage device in association with each other. In addition, the input section is a tablet type input device and the predetermined operation is a writing operation on the input device by using predetermined input characteristics.
When such an image display apparatus is used to read or browse documents such as books, literatures, and medical records, a user often inputs additional information on the documents by handwriting for easy understanding. However, when a certain page of the document is turned with the handwriting information displayed together with the document, the image display apparatus once erases the page where the handwriting information is displayed from the screen to make an image of the next page on the screen, whereby the handwriting information disappears from the screen together with the certain page of the document.
To address this problem, such the image display apparatus can employ a method to store the data of the handwriting information in a storage, read out the stored data after turning a page of the document, put the handwriting information onto the document and then draw the document on the screen again. However, with this method, a reading operation and a process of the data are required every time when pages are turned, which creates a problem that time and effort are required.
As another method, the image display apparatus can employ a method to divide the screen thereof into some areas, and display the handwriting information in an area different from an area in which the document is displayed. However, because the size of the screen of the portable image display apparatus is small, when the small sized screen is divided into a plurality of areas, a problem arises that visibility of the document gets bad or it is difficult for users to perform handwriting input. The present invention seeks to solve the problem.